During spermatogenesis, developing preleptotene spermatocytes residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier (BTB) at stage VIII of the epithelial cycle in adult rat testes, entering the adluminal compartment for further development. Without this timely movement of developing germ cells across the BTB, spermatogenesis will be disrupted, leading to infertility. While this cellular phenomenon pertinent to spermatogenesis is known for decades, the mechanism(s) that regulates BTB dynamics to facilitate germ cells to traverse the BTB is entirely unknown. This by and large is due to the lack of a suitable in vivo model to study BTB dynamics. In this application, the P.I. proposes to develop and extensively characterize a novel model to meet this need. In brief, local administration of a 22-amino acid synthetic peptide based on the second extracellular loop of occludin, a tight junction (TJ)-integral membrane protein at the BTB, to adult rat testes was shown to induce reversible disruption of BTB in the seminiferous epithelium. Also, this event was associated with changes in the expression of several target proteins (e.g., transforming growth factor [unreadable]-3, TGF-[unreadable]3, and tumor necrosis factor a, TNFa) that mimicked the Sertoli cell TJ-barrier restructuring events in vitro. Perhaps the most important of all, this local occludin peptide treatment also induced reversible germ cell loss (in particular spermatids and spermatocytes, but not spermatogonia) from the seminiferous epithelium. The P.I. seeks to extensively characterize this novel in vivo model by delineating the detailed timeline of cellular, molecular and biochemical changes in the seminiferous epithelium correlating with the status of spermatogenesis and the integrity of the BTB. Results of these studies will yield a reliable study model for investigators in the field to understand the mechanism and regulation of BTB restructuring during spermatogenesis. Our primary goal is to develop an innovative in vivo model to study BTB dynamics which is significantly different from currently available study models using toxicants (e.g., cadmium and glycerol). First, the peptide that can induce BTB restructuring is non-cytotoxic. Second and perhaps most importantly, the disrupted BTB can be "resealed", making this model uniquely suitable to study the biology and regulation of BTB re-assembly during spermatogenesis. [unreadable] [unreadable] [unreadable] [unreadable]